This invention relates to liquid carrier fluids for water soluble polymers or gums. This invention also relates to a method for avoiding lump or "fisheye" formation when dry, hydrophilic polymers are added to aqueous systems. This invention also relates to enhancing secondary oil recovery without damaging or substantially reducing the permeability of the porous strata with which it comes into contact. Other aspects as well as the advantages of the disclosed invention will be apparent to those skilled in the art upon reading the following disclosure and claims.
Hydrophilic polymers or gums are widely used in industry. They are used to thicken, suspend or stabilize aqueous systems. These gums can produce gels or act as emulsion stabilizers, flocculents, binders, film formers, lubricants and friction reducers. In each of these applications, the polymers are used to adjust and control the rheological properties of the aqueous system to which they are being added.
For commercial and industrial applications, rapid addition of these gums to water is highly desirable. Doing so, however, often results in the formation of lumps of unhydrated polymer, commonly known as fisheyes. These lumps are gel-like substances, wet on the outside but dry on the inside, that form as a result of the polymer beginning to hydrate before the polymer molecules are dispersed. Once the outer layer of polymer is hydrated, the lump or fisheye often cannot be dispersed even with vigorous mixing. Removal of these lumps results in significant losses of time, material and polymer efficiency.
These lumps are particularly problematic in the oil and gas industry where water soluble polymers are used downhole during drilling, workover, completion, stimulation and reservoir flooding operations. These unhydrated lumps, inert to enzymes, chemical breakers and acids, cause a variety of problems including plugging of the well and permeability impairment of the oil bearing strata.
To avoid lump or fisheye formation and its associated problems, the polymers can be added to the aqueous systems as liquid slurries. A number of methods for accomplishing this, and the compositions prepared thereby, are described in the prior art. Unlike the present invention, they use oil carriers (e.g., mineral or diesel) to suspend and deliver the polymers to the aqueous systems. In addition to the oil carrier fluid, these slurries usually contain clay or clay like particulates which act to viscosify and stabilize the water in oil emulsion. The disadvantages of these carrier systems is that attempts to eliminate the oil, often an undesirable component, result in the substitution of oil by toxic glycol ether. The clay component itself is also oftentimes an undesirable component. This is particularly true in oil and gas field applications where incorporation of the clay into the slurries, which is necessary to keep the polymer in solution, impairs the permeability of the oil or gas bearing strata. This is the very problem caused by the formation of fisheyes that the oil slurry is supposed to eliminate.
U.S. Pat. No. 4,453,979 describes the use of water with a high molecular weight blend of water and polyethylene glycol to disperse hydrophilic gums. European Publication 58 017 describes the use of a water and clay based drilling fluid which contains high molecular weight PEG. PEG ranging in molecular weight from 1000 to 10,000,000, which are solid at room temperature, are mentioned.
The disadvantages of the oil based carders are overcome by the present invention by using a safe, nontoxic, water soluble carrier fluid. In addition to this, the present invention allows the addition of a polymer to aqueous systems with or without mixing that, in the case of a dry polymer, could result in lump or fisheye formation.